The present invention relates to the field of programmable devices, and the systems and methods for programming the same. Programmable devices, such as FPGAs, typically includes thousands of programmable logic cells that use combinations of logic gates and/or look-up tables to perform a logic operation. Programmable devices also include a number of functional blocks having specialized logic devices adapted to specific logic operations, such as adders, multiply and accumulate circuits, phase-locked loops, and one or more embedded memory array blocks. The logic cells and functional blocks are interconnected with a configurable switching circuit. The configurable switching circuit selectively routes connections between the logic cells and functional blocks. By configuring the combination of logic cells, functional blocks, and the switching circuit, a programmable device can be adapted to perform virtually any type of information processing function.
Programmable devices include one or more input/output (I/O) banks for communication with external devices, such as memory devices, network interfaces, data buses and data bus controllers, microprocessors, other programmable devices, ASICs, or any other type of electronic device. Each I/O bank is connected with a number of conductive I/O pins, balls, or other electrical connectors in the programmable device chip package. An I/O bank includes logic for sending and receiving data signals, control signals, clock signals, power and ground signals, or any other type of signal used in conjunction with communications between the programmable device and an external device.
The I/O banks of a programmable device include logic, amplifiers, filters, and other circuits that together can be configured to provide one or more standard interfaces between the programmable device and external devices. Additionally, the I/O banks of a programmable device can be configured to provide custom or proprietary interfaces if required by a particular application.
Typically, a wide range of different programmable devices are designed as part of a programmable device family. The programmable devices within a device family typically have similar architectures but may differ in chip package size and type, the number of I/O pins, the number of logic cells, the number and type of functional blocks and other specialized logic blocks, and/or other characteristics.
In prior programmable device families, the programmable device architecture supports only a fixed number of I/O banks. As a result, programmable devices within the device family may have different amounts of I/O pins per I/O bank. For example, if a programmable device architecture supports 8 I/O banks, a small programmable device within the device family may only have 20 I/O pins per I/O bank, for a total of 160 I/O pins for the programmable device. In contrast, an example large programmable device within the device family may have 70 I/O pins per I/O bank, for a total of 560 I/O pins for the programmable device.
The use of a fixed number of I/O banks and a variable number of I/O pins per I/O bank in a programmable device architecture presents a number of problems. First, most I/O banks can only be configured to support a one interface at a time. As the number of I/O pins per I/O bank increases, any I/O pins not needed for the supported interface are left unused. The unused I/O pins from one or more I/O banks cannot be aggregated to support an additional interface. Thus, as the number of I/O pins per I/O bank increases, the percentage of I/O pins utilized typically decreases. This often forces designers to use programmable devices with even more I/O pins to ensure that there are sufficient I/O pins available to support the required interfaces, which further increases the costs of implementing a design. Additionally, these restrictions on I/O pin usage limit the designers' flexibility in circuit board layout.
Vertical migration is another problem arising from prior programmable device architectures that use of a fixed number of I/O banks and a variable number of I/O pins per bank. Often, designers will develop an initial design for a particular size programmable device within a device family. Subsequent revisions or improvements to the design may require additional programmable device resources. Designers would like to be able to implement the revised design using a larger size programmable device within the same device family without substantial reengineering and testing costs.
However, prior programmable device architectures having a fixed number of I/O banks and a variable number of I/O pins per bank often require substantial reengineering for vertical migration. For example, because the number of I/O pins per I/O bank often increases for a larger devices, the I/O banks of the larger device may not support the same I/O pin assignments as the corresponding I/O banks in the smaller device. Thus, designers must reengineer the device as well as associated circuit boards to account for these differences.
Noise, clock skew, and signal reflection are other problems arising in vertical migration that are caused by the use of a fixed number of I/O banks and a variable number of I/O pins per bank. As the number of pins per I/O bank increase, the total number of active switches and other components associated with I/O pins increases, thereby increasing the amount of noise and signal reflections introduced. Similarly, I/O banks with more I/O pins will have greater amounts of clock skew than smaller I/O banks. Thus, when a design is migrated from a smaller programmable device to a larger programmable device, designers must work to overcome the additional noise, signal reflections, and clock skew introduced by the use of I/O banks with additional I/O pins.
It is therefore desirable for a programmable device architecture to overcome the difficulties normally associated with a fixed number of I/O banks having variable numbers of I/O pins. It is desirable for the programmable device architecture to allow for efficient I/O pin utilization regardless of the total number of I/O pins. It is further desirable for the programmable device architecture to facilitate vertical migration to larger programmable devices while reducing the required reengineering effort. It is also desirable for the I/O banks to have improved performance as compared with I/O banks of prior programmable device architectures.